Lampholders for General-service Incandescent LAMPHOLDERS MADE OF THERMO- PLASTICS, METAL AND PORCELAIN LAMPHOLDERS FOR GENERAL-SERVICE INCANDESCENT The general-service light bulb owes its name to its bulbous shape, which has remained almost unchanged to this day. The tungsten filament contained within the bulb's glass shell, in which there used to be a vacuum but which is nowadays more usually filled with an inert gas, begins to glow as electricity is passed through it. Despite the considerable technical progress that has been made, the typical disadvantages associated with light bulbs still remain. For instance, incandescent lamps mainly radiate heat with no more than 5–10% light output and have a service life of approx. 1000 operating hours. As a result of energy-efficiency regulations in the various regions of the world, the use of all-purpose incandescent lamps has been limited or even banned. Nonetheless, thanks to the many different shapes and surfaces of lamp bulbs, all-purpose incandescent lamps still have a firm place in decorative residential lighting applications and are often an important feature of luminaire designs. Retrofit lamps that comply with energy-efficiency regulations are increasingly being used as a replacement for all-purpose incandescent lamps and use the same lampholder systems found with E12/E14, E26/E27, E39/E40, B15d and B22d bases. VS lampholders for general-service incandescent and retrofit lamps Depending on the operating conditions, lampholders can be made of thermoplastics, metal or porcelain. Metal lampholders are most often used for high-grade decorative luminaires. In accordance with protection class I, metal lampholders must be included in the measures taken to earth the luminaire. Due to their heat resistance, Edison lampholders made of porcelain are frequently used for higher-output lamps. Classic lampholder materials like metal and porcelain are increasingly being displaced by modern thermoplastics. 278